DE2419914C3 - Measuring device for the compensation of disturbances of a connected measuring sensor, in particular its temperature dependence - Google Patents

Description

The invention relates to a measuring device for compensating for disturbance variables of a connected Sensor, especially to compensate for the influence of temperature on the injection pressure and after : k of injection molding machines, where at the input: s DC voltage amplifier intermittently wäh-J predetermined measuring times the variable to be measured and the disturbance variable, as well as that during the respective Measurement time signal derived from the disturbance variable at the compensation input of the DC voltage amplifier pending, with a memory that stores its input value while forming a control loop Compensation input of the DC voltage amplifier feeds, with the at the compensation input last voltage value present is retained during the measurement process

ίο When measuring state variables such as pressure, Temperature, torques on a shaft are the measured values emitted by a sensor generally falsified by disturbance variables. For example, the temperature can be used as a pressure measurement

Disturbance occurs; in the opposite case, the pressure can also occur as a disturbance variable in the temperature measurement. Another example is the determination of the loads or strains on machine parts using strain gauges, the measured values of which are also

if can be falsified by the temperature

When determining the measuring pressure of the plasticized plastic material in injection molding machines than further The example mentioned is that the temperature is a disturbance variable.

Even if in many cases an elimination through bridge and compensation circuits at the measuring location If these disturbing influences are possible, this is not possible in some cases. In particular, Injection molding machines do not have additional compensation devices due to the lack of space for the sensors be added at the measuring location for these purposes. In addition, such circuits occur only within predetermined temperature intervals work satisfactorily, while after exceeding these temperature ranges the temperature disturbance variable the measurement result influenced. The same applies to the other disturbance variables mentioned.

Measuring devices of the type mentioned are already known per se (DT-OS 22 40 766). It deals This means that the temperature changes in

,, o the expansion of the roll stands To distinguish between elongations caused by the slabs when passing through the roll stands will. For this purpose, a compensation voltage is generated, which is approximately the time Change in temperature is proportional. This is subtracted from the voltage, including the corresponds to roll elongation generated by the slabs. The particular disadvantage here is that the change in temperature over time can only be detected approximately.

It is also known (CH-PS 4 96 944) to convert the analog measurement signal into a digital one by means of a converter Convert the signal and with a drift compensator the input of the converter the signal for compensation to feed.

The invention is based on the object of designing a device of the type mentioned in such a way that it can optionally be arranged outside the measuring point, is not tied to predetermined small areas for the elimination of the disturbance variable (s) and no additional sensors for detecting the disturbance variables requires.

According to the invention, this object is achieved by an analog-digital converter for the Gieiciisparinungsvers'ärker downstream voltage-controlled oscillator, a downstream phase detector, to which the frequency of a frequency-stable oscillator is fed as a reference frequency and its output

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inal is fed as DC voltage to the analog memory, which interrupts the control loop during each measurement process. Through these measures wi xl achieve! That when the control loop is closed, the controlled oscillator with its predetermined rumble frequencies? oscillates, * regardless of whether the quantity at its input changes or not. If only the disturbance variable is present at the input during this time, the voltage-controlled oscillator consequently continues to oscillate at this predetermined basic frequency. If the variable to be measured is now also given to the ^{| 0} input of the DC voltage amplifier * with simultaneous interruption of the control loop, then, if the disturbance variable is constant during a sufficiently short measurement time, only the measured value of the M variable to be measured is recorded successive measuring cycles always start from a reference value pending at the compensation input, which is constant during the measurement, but can have a different value from measurement to measurement due to temperature changes, the influence of temperature on the measurement result is eliminated . For this reason, the device according to the invention is insensitive even to changes in the ambient temperature.

In a further embodiment of the invention, the voltage-controlled oscillator is also followed by a frequency counter which displays the measured values and to which a subdivided frequency of the frequency / stable oscillator is fed. This frequency counter is calibrated in bar when measuring pressure, for example, by inputting known voltage values to the DC voltage amplifier, which correspond to certain pressures assigned to the sensor. The control logic of the frequency counter * consists of an emern monostable multivibrator, to which the lower frequency of the oscillator is fed, as a timebase. Muirvbnitor. where the output pulse .le · -, the first —ortosubtiert Muimbrators each time the counter surd ir siren memory over -.--. igen and the output pulse of the r * wxn rionostable Müllenivbrator je-ove;! ·; the Zi ~. <; r delete. By grounding these two rro -'.- stihier Muftiv'bratorer! * ies the well-known one for controlling derange counters

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voltage-controlled oscillator connected to the frequency counter, which has a further input for the Output voltage of the frequency stable oscillator 14 has.

The output voltage of the phase detector 13 is as long as the switch 15 is open. The closed switch 16 of the analog memory 17 is fed to the input 11 of the DC voltage amplifier. This causes a feedback in the sense that in this position of the two switches 15 and 16 the controlled oscillator always continues to oscillate at the predetermined fundamental frequency f \ . If the input signal changes in this switch position (switch 15 open, switch 16 closed) as a result of pressure and / or temperature changes at input 9 of DC voltage amplifier 10, this feedback ensures that the voltage-controlled oscillator continues to operate at its predetermined fundamental frequency f \ swings on.

To prepare for a measurement, at the beginning of each injection cycle (FIG. 3), namely before the Form a pressure builds up (pressure zero), the switch 15 is closed and the switch 16 is open for the duration of a measurement. As a result, the analog memory 16 receives the last input value during the measurement time at the compensation input 11 of the DC voltage amplifier of the compensation voltage can stand and the controlled oscillator 11 as long as its base frequency A, continues to oscillate when there is no change in the signal present at input 9 of DC voltage amplifier 10 he follows.

If the input signal changes as a result of a change in pressure, the frequency of the changes voltage-controlled oscillator output voltage proportional to this pressure change.

The output of the voltage-controlled oscillator 12 is followed by the frequency counter 20, which is shown in FIG Pressure is calibrated.

To calibrate the frequency counter with certain pressures, output voltage values are assigned to it of the sensor in input 9 of the DC voltage amplifier and the display of the frequency counter calibrated in this way.

The output from the oscillator 14 is shown in FIG Oscillator frequency in its asymmetrical form as the time base to the input of the first monostable Multivibrator 22 supplied, the output pulse of which carries out the memory transfer of the count and at the same time controls the second monostable multivibrator 23 with its rear flank, which with his Output pulse clears the counter. With these two monostable multivibrators, the gate circuit is not required at the input of the counter and the balancing of the asymmetrical time base signal. Furthermore has this Circuit has the advantage that there is a waiting time from measuring cycle to measuring cycle, so that the Restoring the information, d. h-, the alternating The sequence of measuring - displaying - measuring is omitted and each time base pulse brings a new measurement.

Due to the lack of primary circuit and Time symmetry circuit is a compensation of switching operations, the display in a known manner falsify the measurement result by ± one bit, superfluous. At the same time, the alternating one is omitted Switching between measurement and display in the counter, so that a measured value in the Display appears. Since the balancing is not required, the applied time base frequency have any duty cycle.

By swapping the inputs »measurement frequency« and »time base frequency« the function of frequency measurement becomes switched to the time measurement function. In Fig. 3, the measurement method is exemplified by one

ίο Injection molding machine explained. The time is indicated on the abscissa and the pressure profiles resulting from each injection molding process are indicated on the ordinate. Between the successive pressure profiles there is a zero pressure in the injection mold for a certain time. During this time, the injection mold is extended, the injection molded part is formed and the injection mold is closed again. Subsequently, the injection pressure is exerted on the plasticized mass to be injected by acting on the hydraulic control (not shown) in FIG. 2, so that the next pressure curve shown in the drawings occurs. Each measuring process is initiated by preparing the device for the measurement by closing the switch 15 (FIG. 1) when the pressure is zero between two pressure profiles. The switch is closed at time y or y " and opened again at time χ or x".

The times y and λ "at which the switch is closed or opened again are shown in FIGS. 3 and 4. A temperature profile is also shown schematically, the temperature increasing by about 32" C. over a period of about 5 minutes changes during the start-up of the injection molding machine (heating of the injection device).

This opens and closes the switch 15 at the beginning or at the end of a measurement or the opening of switch 15 between two measurements and corresponding closing and opening of switch 16 what is achieved is that the device adjusts itself and thereby eliminates the disruptive influence of temperature.

F i g. 5 shows a control device for switching from injection pressure to holding pressure, which is based on the principle of FIG Device according to FIG. 1 is based.

As shown in FIG. 5, the frequency counter 20 is followed by a digital comparator 23, the further one Has inputs 24, at which setpoints for the injection pressure are pending, which by actuating the corresponding

The corresponding selector switches 25,26,27 in the comparator are compared with the actual values A , with a switching signal from injection pressure to holding pressure being present at the output of the comparator when the setpoint entered is reached or exceeded by the actual value (AB).

that is fed to the injection molding machine. Otherwise, the control device corresponds to FIG. 5 of those in Fig. 1.

With the device according to the invention, for. B. at some point in a pressurized a pressure increase can be measured when the system is standing Time the pressure difference is measured. The pressure that is already present is reduced during the phase »Rules« are straightened out and thus related to zero and used as the starting point for the measurement.

In addition 5 sheets of drawings

Claims (5)

Patent claims: 1. Measuring device for compensating for disturbance variables from a connected sensor, in particular to compensate for the influence of temperature on the injection pressure and holding pressure of injection molding machines, being at the input of a DC voltage amplifier intermittently during given Measuring times the variable to be measured and the disturbance variable, as well as during the respective Measurement time derived from the disturbance signal at the compensation input of the DC voltage amplifier with a memory that his Input value with the formation of a control loop to the compensation input of the DC voltage amplifier with the last voltage value present at the compensation input during of the measuring process is retained, characterized by a DC voltage amplifier (10) a voltage-controlled oscillator (12) connected downstream as an analog-digital converter, this downstream phase detector (13), which is the frequency of a reference frequency frequency-stable oscillator (14) is supplied and its output signal as DC voltage to the Analog memory (17) is supplied, which interrupts the control loop during each measurement process. 2. Measuring device, characterized by a voltage-controlled oscillator in addition downstream frequency counter (20) which displays the measured values and which has a subdivided frequency of the frequency-stable oscillator is supplied. 3. Measuring device according to claim 2, characterized in that the control logic of the frequency counter from a monostable multiviorator (22), to which the subdivided frequency of the oscillator is fed as a time base frequency, one of these downstream further monostable multivibrator (23) is connected downstream, there is Output pulses of the first monostable M lltivibrators each the counter reading in a memory transmitted and the output pulses of the second monostable multivibrator in each case the counter Clear. 4. Device according to claims 1 to 3, characterized by the DC voltage amplifier additional downstream peak value memory (21), which follows the frequency counters Reaching the maximum value of the measured variable stops. 5. Device according to one or more of the preceding claims, characterized in that the frequency counter is followed by a digital comparison device which compares the signals A supplied as actual values with predetermined setpoint values B and which in each case emits a control command when A = B or A> B .